Package structure for surface acoustic wave device, and surface acoustic wave device

ABSTRACT

A package structure realizing a size and/or thickness reduction and suitable for packaging a surface acoustic wave element is provided. The package structure for solving the above challenge includes a base having a thick floor on which to place a surface acoustic wave element and a thin floor on which to place an electronic component, the surface acoustic wave element and the electronic component being mounted close to each other on the plane coordinate system. In addition, in the package structure described above, the difference in height between the thin floor and the thick floor is the same as, or larger than, the thickness of the electronic component mounted on the thin floor.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation of U.S. application Ser. No. 11/878,539 filed onJul. 25, 2007, which is a Continuation of U.S. patent application Ser.No. 11/354,182 filed Feb. 15, 2006. The entire disclosures of the priorapplications are hereby incorporated by reference herein in theirentirety. This application also claims priority from Japanese PatentApplication No. 2005-58616, filed in the Japanese Patent Office on Mar.3, 2005, the entire disclosure of which is hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a package structure for a surfaceacoustic wave device and a surface acoustic wave device, and moreparticularly to a package structure for a surface acoustic wave deviceand a surface acoustic wave device that are suitable for reduction of apackaged surface.

BACKGROUND

There are strong demands for reduction of the size and/or the thicknessof piezoelectric devices used in information-communication equipmentsand other equipments. The developing side has responded to such demandsthrough development of various sorts of piezoelectric devices that areintended for reduction of the size and/or the thickness.

Basically, a piezoelectric device is composed of a piezoelectricresonator element, an electronic component such as an integrated circuit(IC) that performs temperature compensation, resonance control and/orother operations for the piezoelectric resonator element, and a packagein which the piezoelectric resonator element and the IC are packaged.

As shown in FIGS. 3A and 3B, a common structure of a piezoelectricdevice that is intended for a reduction of the size includes an IC 3placed on the floor of a package 4 that is formed in tiers and apiezoelectric resonator element 2 placed on a tier over the IC 3. Insuch a structure, however, it is necessary to provide a resonating spacefor the piezoelectric resonator element 2, while also providing aclearance between wires 5 for wire-bonding to package the IC 3 and thepiezoelectric resonator element 2. This causes a major problem inreducing the thickness of a piezoelectric device 1 having the structuredescribed above.

On the other hand, among piezoelectric devices that are intended forreduction of the thickness is one disclosed in Patent Document 1. Asshown in FIGS. 4A and 4B, in the piezoelectric device disclosed in thedocument, supporting portions (protrusions in Patent Document 1) 6 areformed inside the package 4 to serve as supporting portions for thepiezoelectric resonator element 2, and the piezoelectric resonatorelement 2 is placed side by side with the IC 3. Such a structure of apiezoelectric device allows a height-lowering of the device byprecluding the necessity to allow for a vertical clearance between thepiezoelectric resonator element 2 and the IC 3.

The piezoelectric device disclosed in Patent Document 1 is inferior insize reduction, but superior in thickness reduction, to the one shown inFIGS. 3A and 3B. Furthermore, since the piezoelectric resonator elementand the IC can be mounted simultaneously or serially in the package, theprocess of hardening the adhesive used for mounting the two componentscan be performed at a time as one common process, an advantage thatallows an improvement in the productivity. In addition, packagedconditions of the two components can be checked by observing from thesurface, even after they have been mounted.

[Patent Document 1] JP-A-H9-83248

Both the piezoelectric device shown in FIGS. 3A and 3B and the onedisclosed in Patent Document 1 may be very effective in reducing thesize and/or the thickness of the device when an AT cut or other quartzcrystal resonator element is employed as a piezoelectric resonatorelement.

However, generally speaking, the piezoelectric device in FIGS. 3A and 3Band in Patent Document 1 are not suitable for use in cases in which asurface acoustic wave element (SAW element) is employed as a resonatorelement, a SAW element being thicker and heavier than an AT cut or otherquartz crystal resonator element. Both of the piezoelectric devicesshown in FIGS. 3A, 3B, 4A and 4B have small supporting areas for aresonator element. Therefore, when a weighty SAW element is mounted, theresonator element undergoes the risk of being deformed by its ownweight. It may also be possible to draw upon the piezoelectric deviceshown in FIGS. 4A and 4B as a guide and provide adequate supportingareas for the resonator element by placing the element and the IC on thesame level. However, this tends to deform the package itself because thepackage floor of the piezoelectric device shown in FIGS. 4A and 4B isthin. Thus, the SAW element supported by the package floor is likely tobe affected by deformation of the package.

An object of the invention is to provide a package structure for asurface acoustic wave device and a surface acoustic wave device thatrealize a reduction in the size and/or the thickness and that issuitable for packaging a surface acoustic wave element.

DISCLOSURE OF THE INVENTION

A package structure for a surface acoustic wave device according to theinvention, which is intended for achieving the above object, is thestructure of a package that is packaged with a surface acoustic waveelement and an electronic component, the package structure having a basethat includes a thick floor on which the surface acoustic wave elementis placed and a thin floor on which the electronic component is placed,and the surface acoustic wave element and the electronic component beingmounted close to each other on the plane coordinate system. In otherwords, a package structure is provided for a surface acoustic wavedevice that includes a surface acoustic wave element and an electroniccomponent. The package structure includes a base defining first andsecond areas, the surface acoustic wave element being disposed at thefirst area and the electronic component being disposed at the secondarea. The first and second areas are adjacent relative to a first plane.The base has a greater thickness at least a portion of the first areathan at the second area relative to a second plane that is perpendicularto the first plane.

Through such a structure, a sufficient area can be provided for mounting(bonding) the surface acoustic wave element. At the same time, thepackage is prevented from being easily deformed as well as conveying adeformation that occurs in it, because the floor on which the surfaceacoustic wave element is placed is thick. The structure also allowspackaging (wire-bonding) to be performed after all the components havebeen die-attached, because the surface acoustic wave element and theelectronic component do not vertically overlap each other. Moreover,since the wire-bonding process can be performed after all the componentshave been mounted, the adhesive has been hardened through heating andannealing has been performed, it is no more necessary to allow for aeutectic to occur between bonding wires and bonding pads, thus allowingannealing to be performed at an adequately high temperature.Furthermore, packaging of the components on two levels, on a thick floorand a thin floor, prevents a collet as a jig from touching adjacentcomponents. Therefore, clearance between components in the mounting areacan be reduced, thus realizing a size reduction of the device.

It is preferable that the difference in height between the thin floorand the thick floor is the same as, or larger than, the thickness of theelectronic component mounted on the thin floor. Such a structure allowspart of the surface acoustic wave element to overlap the electroniccomponent. In other words, a difference in thickness of the base betweenthe at least a portion of the first area and the second area in thesecond plane is the same as, or larger than, a thickness of theelectronic component in the second plane.

A surface acoustic wave device according to the invention, which isintended for achieving the above object, includes a surface acousticwave element and an electronic component that are packaged inside itspackage, the device having a base that includes a thick floor and a thinfloor, the surface acoustic wave element and the electronic componentbeing placed close to each other on the plane coordinate system, thesurface acoustic wave element being mounted on the thick floor and theelectronic component being mounted on the thin floor. In other words, asurface acoustic wave device is provided that includes a surfaceacoustic wave element; an electronic component; and a package forpackaging the surface acoustic wave element and the electroniccomponent. The package includes a base defining first and second areas.The surface acoustic wave element is disposed at the first area theelectronic component is disposed at the second area. The first andsecond areas are adjacent relative to a first plane. The base has agreater thickness at least a portion of the first area than at a secondarea relative to a second plane that is perpendicular to the firstplane.

Such a structure allows the surface acoustic wave element to be mountedin a stable manner while preventing the package from being easilydeformed or conveying a deformation that occurs in it, because the floorthat is mounted with the surface acoustic wave element is thick. Thestructure also allows packaging (wire-bonding) to be performed after allthe components have been die-attached, because the surface acoustic waveelement and the electronic component do not vertically overlap eachother. In addition, since the wire-bonding process can be performedafter all the components have been mounted, the adhesive has beenhardened through heating and annealing has been performed, it is no morenecessary to allow for a eutectic occurring between bonding wires andbonding pads, and, thus, annealing can be performed at an adequatelyhigh temperature. Furthermore, as the components can be packaged on twolevels, on a thick floor and a thin floor respectively, a collet used asa jig for mounting the components is prevented from touching adjacentcomponents. Therefore, clearance between components in the mounting areacan be reduced, thus realizing a size reduction of the device.

In a surface acoustic wave device described above, it is preferable thatthe difference in height made between the thin floor and the thick flooris the same as, or larger than, the thickness of the electroniccomponent mounted on the thin floor. Such a structure allows part of thesurface acoustic wave element to overlap the electronic component. Inother words, a difference in thickness of the base between the at leasta portion of the first area and the second area in the second plane isthe same as, or larger than, a thickness of the electronic component inthe second plane.

It is also preferable that the surface acoustic wave element and theelectronic component are mounted in positions such that the surfaceacoustic wave element does not vertically overlap the electroniccomponent. Through an adjacent placement of the surface acoustic waveelement and the electronic component based on the above condition, afurther reduction in size will be realized in addition to theadvantageous effects described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams showing the structure of a surface acousticwave device according to the invention.

FIGS. 2A, 2B and 2C are diagrams showing the manufacturing stream forthe surface acoustic wave device according to the invention.

FIGS. 3A and 3B are diagrams showing the structure of a related artpiezoelectric device intended for a reduction of the size.

FIGS. 4A and 4B are diagrams showing the structure of a related artpiezoelectric device intended for a reduction of the thickness.

PREFERRED EMBODIMENTS IMPLEMENTING THE INVENTION

A package structure for a surface acoustic wave device and a surfaceacoustic wave device according to the invention will now be describedwith reference to the drawings, wherein the embodiment described belowonly partly represents the embodiments according to the invention.

FIGS. 1A and 1B are diagrams showing a piezoelectric device according tothe embodiment, wherein FIG. 1A is a plan view and FIG. 1B is afront-sectional view.

A surface acoustic wave device 10 according to the embodiment basicallyincludes a surface acoustic wave element (SAW) 12, an electroniccomponent 14 and a package 15 in which the SAW element 12 and theelectronic component 14 are packaged.

As shown by the front-sectional view in FIG. 1B, the package 15 iscomposed of a base 16 on which packaged components are mounted and a lid17 to seal the opening of the base 16.

The base 16 includes a thin floor 16 a and a thick floor 16 b that serveas surfaces on which to mount the packaged components. According to theinvention, particularly, the thin floor 16 a serves as a surface onwhich to mount the electronic component 14 and the thick floor 16 bserves as a surface on which to mount the SAW element 12. Advantageouseffects obtained with such a structure of the package 15 include theones described below.

First, through a vertical difference made between the surfaces on whichthe electronic component 14 and the SAW element 12 are respectivelymounted (placed), interference between the components can be avoided atthe time when they are mounted. Therefore, a narrower clearance can berealized between the components than in the case where they are placedside by side on a plain floor. Thus, consideration is only necessary fora clearance between a jig (collet) for mounting the components and theframe of the base 16.

Second, through use of the thick floor 16 b to serve as a surface onwhich to mount the SAW element 12, rigidity increases in the package(base 16) 15, thereby making it difficult for the surface to bedeformed. Moreover, since a sufficient area to match the size of the SAWelement is provided for mounting the element, even the heavy SAW elementis free from being deformed by its own weight.

Also, when the base 16 packaged with both the electronic component 14and the SAW element 12 is observed from the top surface (See FIG. 1A),the packaging terminals (bonding pads) of both the electronic component14 and the SAW element 12 can be checked. Therefore, it is allowed as amanufacturing process to simultaneously perform heating on theelectronic component 14 and the SAW element 12 after they have beenmounted (bonded), so as to harden adhesive 24 and perform annealing.Furthermore, packaging can be accomplished by simultaneously performingwire-bonding after finishing the processes of hardening the adhesivesand annealing.

In addition, as described above, there is no risk that a eutectic occursbetween the bonding wires 18 and the bonding pads 20 through a hightemperature, because wire-bonding can be performed after the processesof hardening the adhesive 24 and annealing.

It is demonstrated through the applicant's experiments that a eutecticoccurs in 30 minutes at the terminal area between the gold wires forwire-bonding and the aluminum bonding pads when the area is heated at atemperature within the range of 260° C. to 270° C. On the other hand,the surface acoustic wave device is heated at about 270° C. for 3 to 4hours for hardening of the adhesive 24 and annealing. Thus, there is therisk that the eutectic occurring between the wires and the padsprogresses and creates a serious defect for finished products. However,such a defect can be avoided for a SAW device 10 having the package 15of the above structure.

Furthermore, a difference in height is made between the mounted surfacesof the SAW element 12 (thick floor 16 b) and the electronic component 14(thin floor 16 a) so as to be the same as, or larger than, the thicknessof the mounted electronic component. Therefore, part of the SAW element12 can be placed so that it overlaps the electronic component 14. Inthis case, too, a similar effect as above can be achieved if the bondingpads 20 of the electronic component 14 can be identified by observingthe base 16 from the top surface after it has been mounted with thecomponents. In this way, the packaging area can be reduced for eachcomponent and a more compact surface acoustic wave device 10 can berealized.

The SAW element 12 described above is made of a piezoelectric materialsuch as quartz crystal, Lithium Tantalate or Lithium Niobate, on whichmetal patterns are made to provide an interdigital transducer (IDT), areflector, and so on.

The electronic component 14 refers to an integrated circuit (IC) forcontrolling the oscillation of the SAW element 12, but mounting also acondenser, and/or the like, (not illustrated) besides the IC does notconstitute any deviation from the present embodiment.

A SAW device 10 according to the embodiment, which includes the abovecomponents, is manufactured by a process illustrated in FIG. 2.

First, a base 16 of a package 15 is formed by sintering, or anothermethod of the sort. Commonly, the base 16 is made by depositing and thensintering multiple substrates, but it may also be formed by anothermethod. It is preferable that internal patterns 22 are provided insidethe base 16 at the stage of formation (See FIG. 2A).

Next, adhesive 24 is applied to a thin floor 16 a of the package, ontowhich an IC 14, being held by suction by means of a collet, is bonded.Then, the adhesive 24 is applied to a thick floor 16 b, onto which anSAW element 12, being held by suction by means of a collet, is bonded.When the SAW element 12 is bonded, the package size can be reduced ifthe SAW element and packaging terminals (bonding pads) 20 of the IC 14are placed close to one another to the extent that they do not overlap.After the IC 14 and the SAW element 12 have been bonded to the base 16,they are heated together with the base 16 so that the adhesive 24 ishardened and annealing is performed on the SAW element 12 (See FIG. 2B).

After the heating process is over, the IC 14 and the SAW element 12 arepackaged on the base 16 through wire-bonding (See FIG. 2C).

After the above processes have been finished, the opening of the base 16is sealed with a lid 17 to complete the SAW device.

In FIG. 1 and FIG. 2, the thin floor represents only the surface onwhich to mount the IC as an electronic component (including theclearance area for the collet as a jig), but it may also represent allexcept for the thick floor on which to mount the SAW element representsthe thin floor.

1. A surface acoustic wave device in which a surface acoustic waveelement and an electronic component are mounted inside of a package,wherein the package is provided with a base including a thick bottomportion and a thin bottom portion, the surface acoustic wave element ismounted on the thick bottom portion, and the electronic component ismounted on the thin bottom portion, and when the base is seen in a planview, at least part of the surface acoustic wave element overlaps thethin bottom portion.
 2. The surface acoustic wave device as set forth inclaim 1, wherein a height difference between the thin bottom portion andthe thick bottom portion is greater than or equal to a thickness of theelectronic component.
 3. The surface acoustic wave device as set forthin claim 1, wherein when the base is seen in a plan view, a bonding padformed on a surface of the base opposite to a surface on which theelectronic component is mounted does not overlap the surface acousticwave element.
 4. The surface acoustic wave device as set forth in claim3, wherein one end of a bonding wire is connected to the bonding pad.